Receivers in communications systems traditionally were not designed to handle any interference, i.e. they were single user receivers. Since the receiver could not handle interference, communication systems were designed to avoid interference. This typically has been accomplished through the orthogonal scheduling of transmitting users and as part of multiple-access communication schemes, such as FDMA, TDMA, and CDMA, where it is intended to direct users to transmit in a non-interfering or orthogonal manner.
Interference can come in a number of different forms, both internal and external to the communication system. In a cellular communications environment there may be intercellular interference, i.e., interference that is caused by transmitters of a different, usually adjacent, cell. In addition, there may be intracellular interference, i.e., interference that is caused by transmitters of the same cell. In addition to scheduling and multiple access schemes to try and prevent interference, power control techniques are used in a variety of ways to improve the performance of the communication systems. Commonly, power control is used to reduce the effects of intercellular and intracellular interference, and more specifically “near-far” problems, by coordinating transmitters, to transmit such that their powers are nearly the same as received by the receiver, and as such, one transmission is not obfuscating another because it is received at such a greater power.
However, due to the demand for higher spectral efficiency, interference and receivers that can handle interference have become increasingly important, most notably receivers with Multi-User Detection capabilities.
Multi-User Detection (MUD) works by exploiting dimensionality between multiple interfering signals. The dimensionality may occur naturally between interfering signals but may also, as an aspect of the subject matter described herein, be purposely introduced in order to create advantageous situations for the MUD. The dimensionality can take the form of any difference between the received signals that can be exploited by the MUD to more reliably decode the interfering signals. Techniques to create orthogonal dimensionality between signals by design are widely employed with varying multiple access schemes, such as TDMA, FDMA, CDMA, and OFDMA. However networks do not attempt to direct a transmitter in real time to adjust transmit parameters in order to create the dimensionality between interfering signals short of scheduling an interfering transmitter to transmit at a different orthogonal non-interfering time-slot or frequency.
Multiple-input and multiple-output (MIMO), generally speaking, involves the use of multiple antennas at both the transmitter and receiver to improve communication performance. MIMO technology offers significant increases in data throughput and link range without additional bandwidth or increased transmit power. It achieves this goal by spreading the same total transmit power over the antennas to achieve an array gain that improves the spectral efficiency and/or to achieve a diversity gain that improves the link reliability. MIMO results in multiple signals that must be decoded and therefore can benefit from exploiting dimensionality between the multiple signals.
Although techniques have been provided to handle interference, it is desired to provide improved techniques for both managing interfering signals and better utilizing available resources.